SPDSS_Task59-2_Irrigation Water Requirements at Climate Stations

• Title: SPDSS Task 59.2 - Irrigation Water Requirements at Climate Stations
• Description: SPDSS Task 59.2 – This memorandum presents the approach and results from the completion of the following Task 59 subtask: Using calibrated crop coefficients, estimate the irrigation water requirement for common crops grown at the key climate stations identified in Task 53.
• Decision Support - Doc Type: Task Memorandum
• Date: 3/24/2005
• DSS Category: Consumptive Use
• DSS: South Platte
• Basin: South Platte
• Contract/PO #: C153954
• Grant Type: Non-Reimbursable
• Bill Number: SB01-157, HB02-1152, SB03-110, HB04-1221, SB05-084, HB06-1313, SB07-122
• Prepared By: Leonard Rice Engineering

Approach
The SPDSS irrigated acreage assessment for 2001 shows the crop types listed in Table 1 as
being prominent throughout the SPDSS study area, and grown specifically in the Water Districts
shown.
Table 1
Irrigated Crop Types throughout the SPDSS Study Area
T
C Water District
rop
ype 1 2 3 4 5 6 7 8 9 23 47 48 64 80
Alfalfa X X X X X X X X X
Corn Grain X X X X X X X X
Dry Beans X X X X X X X
Grass Pasture X X X X X X X X X X X X X X
Small Grains X X X X X X X X
Sugar Beets X X X X X X X
In addition, there are also relatively minor amounts of orchard and vegetables grown throughout
the SPDSS study area. Based on our research, crop coefficients for the ASCE Standardized
method are not available for orchard or vegetables. Therefore calibrated coefficients were not
developed for these crop types and unadjusted TR-21 modified Blaney-Griddle crop coefficients
will be used to represent these crops in the historical consumptive use analyses.
Crop irrigation water requirement (IWR), the potential consumptive use less effective
precipitation, was determined using the calibrated crop coefficients at the locations of the key
climate stations for the crop types identified in Table 1. The original Blaney-Griddle method
was used with the calibrated crop coefficients for the High Altitude Region and the modified
Blaney-Griddle method was used with the calibrated coefficients for the Upper Plains and Lower
Plains Regions to estimate potential consumptive use. Effective precipitation was estimated
using the SCS effective rainfall method outlined in TR-21. The following StateCU input files
were used for the climate station scenario:
^ Filled climate data sets generated in Task 53.2
^ Calibrated crop characteristic file generated in Task 59.1
^ Calibrated crop coefficient file generated in Task 59.1
^ Crop pattern files with 1 acre of each crop type
Results
The average annual irrigation water requirement estimated by crop type at associated key climate
stations is shown in Table 2 for the period 1950 through 2003.
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